The present invention relates to a device for removing dust from pharmaceutical tablets or capsules. Such devices are used in the pharmaceutical industry for removing from tablets or capsules unwanted medicine powder dust that covers them after their manufacturing process, by compressing or encapsulating this powder. The device for removing dust is thus located in the production line of said tablets or capsules, between a manufacturing devices, by compressing or encapsulating medicine powder, and a conditioning device of these tablets or capsules after removal of their dust.
A prior art dust removal device comprises a dust removal column, generally made of stainless steal, comprising a pharmaceutical tablets or capsules conveying ramp having a shape of an ordered helicoid and enrolled around a central cylindrical element. The ramp comprises a base, an internal edge by which said ramp is fixed to said central element of the column, generally by continuous or point by point welding of said edge from the bottom to the top of the central element, and a peripheral edge. This edge delimitates with the central cylindrical element a conveying channel for tablets or capsules. The column comprises at its bottom an inlet for feeding tablets or capsules in the channel and at its top an outlet for discharging said tablets or capsules from said channel. This column is arranged to be mounted at its bottom, for example by means of nuts, to a motor bloc comprising a motor, for examples an oscillating electromagnetic motor, which when it is switched on, transmits an oscillating movement to the column, which leads tablets or capsules from the bottom to the top of said column, through the channel delimitated by the conveying ramp. Slits are provided at regular distances in the central cylindrical element of the column, contiguously to the base of the ramp and the central cylindrical element is depressed thanks to an aspiration means so that the powder dust that covers tablets or capsules is aspirated through said slits into the central cylindrical element and thereby is removed from the device. Alternatively, the base of the ramp is provided in its radial direction with openings having a diameter lower than that of the tablets or capsules from which dust needs to be removed, these openings being located contiguously to said slits, which themselves are arranged below said base. In this embodiment, cups are disposed below said openings, between the base of the ramp and each slit in the central cylindrical element, in order to aspirate powder dust from tablets or capsules through said openings and to guide this dust through said slits into the central cylindrical element for removing it from the device. The column is surrounded by a tubular enclosure closed at its top, generally made of stainless steal or of a plastic material, whose internal diameter is larger than the outer diameter of the dust removal column and which is removably mounted to the motor bloc of the column, for example by means of nuts or clips, in order to create a confinement space around said column, in order to avoid that tablets or capsules could escape the device and that medicine dust could then spread into the ambient atmosphere. Indeed in such a device, the conveying ramp is not leaktight with respect to the tablets or capsules, which therefore can escape this ramp during their conveyance by bouncing above the peripheral edge of said ramp, which therefore is not constitutive, is not part, of a conveying conduit whose walls would be leaktight with respect to said tablets or capsules. The tablets or capsules dust aspiration means may also be located inside the enclosure, between the latter and the column, eg at its bottom, so that aspiration is performed by depressing the inner space of said enclosure.
Such a conventional device has several disadvantages. Firstly, its construction is complicated since it requires the conveying ramp to be welded to a central cylindrical element, this being a time consuming and difficult task. It also requires a confinement enclosure to be provided to the column for insulating it from the ambient atmosphere, such an enclosure being a separate element from the column, so that such a conventional column cannot be dismounted from the motor bloc of the dust removal device without previously dismounting said enclosure, thereby exposing to the ambient atmosphere tablets or capsules and/or their dust still present in the column if the latter has not previously been cleaned.
Besides, the diameter of the central cylindrical element of such a device may be larger than a quarter of the diameter of the dust removal column, this first diameter being determined both by the aspiration efficiency required through this cylindrical element for achieving sufficient dust removal of the conveyed tablets or capsules and by the rigidity of the column to be achieved for maintaining the integrity of the device. Though, for a given diameter of the column, the diameter of the central cylindrical element determines the dust removal capacity of said column. This capacity is also determined by the height of the peripheral edge of the conveying ramp. Indeed, the thickness of the layer of tablets or capsules that can be conveyed and dust removed by the device needs to be lower than said height, otherwise tablets or capsules would protrude from the ramp and then rest at the bottom of the column without being dust removed.
During the convey of tablets or capsules along the ramp of the column and despite the aspiration of the powder dust which covers them through the slits of the central cylindrical element of said column, dust settles at the column surface and at the internal face of its enclosure. After a certain period of time, the accumulation of this dust becomes excessive and it is then essential to remove it from the surfaces it covers, by cleaning the latter. This is essential as well when tablets or capsules having a different composition than those previously conveyed by the device have to be introduced therein for dust removal, in order to avoid any contamination of the new tablets or capsules by powder dust having a different composition. Such a cleaning can be handmade, by dismounting the enclosure of the device and cleaning its internal surface as well as the column, for example by means of a soft textile, filled with an appropriate detergent if suitable. This cleaning technique is time consuming, namely because it requires the enclosure of the device to be dismounted and it is furthermore burdensome and sometimes insufficient. It may be possible to replace in the device the column and the enclosure to be cleaned by a clean column and a clean enclosure, when one wishes to switch from dust removal of tablets or capsules of a given composition to tablets or capsules of another composition, in order not to interrupt the manufacturing/dust removal/conditioning line during the whole cleaning operation of such a column and enclosure. However, dismounting the enclosure of the device for dismounting the column, and dismounting the latter, inevitably liberates powder dust in the ambient atmosphere as well as on the motor bloc of the device, which causes a risk of contamination by this dust of tablets or capsules of another composition having to be conveyed in the clean column and enclosure replacing those which need to be cleaned.
In an attempt to overcome these disadvantages related to manually cleaning such a dust removal device, it has been suggested by prior art references to provide said device with a self cleaning system. For example, according to EP patent n° 1322533 B1, the disclosed device is provided with sprinklers that spread pressurized water with detergent within the confinement space of the column defined by the enclosure of the device, either from inside its central cylindrical element through openings suitably provided therein, or from outside its enclosure through such openings provided therein. The device is then further provided with a collecting element arranged for removing water from said device. For drying the inside of the device after its cleaning, the referred patent also discloses to connect a source of hot pressurized air or a vacuum pump to the device.
Even though such a self-cleaning device is a breakthrough compared to manually cleanable conventional devices for removing dust from pharmaceutical tablets or capsules, it does not avoid other disadvantages of such devices than those related to their difficult cleaning and even as far as cleaning is concerned, it does not provide an optimal solution to the problem of cleaning such devices.
Indeed, the cleaning system according to said patent is relatively complicated since it requires that a network of sprinklers is distributed within or around the column of the dust removal device. Besides, the quality of the achieved cleaning is not optimal since the cleaning efficiency of water jets spread by the sprinklers depends on the location of the parts of the device that are raised by these jets relatively to their spreading location. In particular, a groove is generally present between the internal edge of the conveying ramp and the central cylindrical element of the column, to which element said edge is fixed, and powder dust tends to agglomerate in this groove, which is especially hard to perfectly clean with water jets spread by said sprinklers. Actually, achieving a perfect cleaning of the column requires to dismount the enclosure and to finish the cleaning manually. Therefore, the disadvantage of such a manual cleaning is not entirely avoided by the disclosed self-cleaning device.